This little patch adds a periodically-requested convenience variable 
whose value is the current thread.  It's handy in scripts and 
conditionals, since the GDB-assigned thread id is unpredictable.

Although the original request was for "$thread", it might be better to 
make it "$_thread" instead, so as not to interfere with possible use in 
existing scripts.  But I'll only change it if I get enough votes in 
favor. :-)

Stan

2010-06-13  Stan Shebs  <stan@codesourcery.com>

    * thread.c (thread_id_make_value): Make a value representing the
    current thread.
    (_initialize_thread): Create $thread.

    * gdb.texinfo (Debugging Programs with Multiple Threads): Describe
    $thread.

    * gdb.threads/thread-specific.exp: Add tests of $thread.